Process and apparatus is disclosed for providing a chemical reaction between calcium oxide containing grit particles to produce calcium hydroxide and heat, capturing the heat of hydration and using it to preheat water initially at ambient temperature, to rise to an elevated temperature to increase the amount of lime present in the water to a supersaturated lime suspension level, with the chemical reaction running to completion, followed by cooling. Heat from a water jacket may be used to raise the temperature in the lime slaker. A process and apparatus is also provided for dissolving scale on internal surfaces of a lime slaker, a lime aging tank, grit separation device and piping and dosing sub-systems, by adding acid into the system with rinse water. A pressurized delivery system that is substantially closed to the atmosphere delivers treating doses of slaked lime slurry under sufficient pressure conditions to maintain a relatively constant back pressure, by means of valving.